Recently, needs of antistatic agents are increasing not only for displays or optical materials but in a wide range of areas including food-related areas. Surfactants or metal oxides are known as antistatic agents, but it is believed that a polymer-type antistatic agent which has excellent transparency and can be expected to have permanent stability is preferred when taking into account a wide application range. Further, as for needs of antistaticity in a composition, awaited is an antistatic agent that functions effectively with a small addition amount which do not impair the composition properties.
As polymer-type antistatic agents, those comprising polyethylene oxide, or those having an ammonium salt structure, or an alkali metal salt structure of acid are known (Patent Documents 1 and 2).
However, for those comprising polyethylene oxide, a high antistatic effect cannot be expected, and it is sometimes necessary to add lithium salt, etc. to improve the effect. Further, polymers comprising ammonium have a limited mobility, and the antistatic property has a tendency to be lower as compared to those in which ammonium is present as a counter cation. The surface resistance level of the film surface using those polymers is for example about 109Ω/□, and a further high performance is awaited. When the ammonium salt units are increased in order to improve this situation, it becomes water soluble, and problems of durability after film forming occur, and when using this polymer in a composition, drawbacks such as bad compatibility arise. Further, to improve the antistatic effect of a composition comprising these polymers, it is necessary to increase the polymer content, and drawbacks are pointed out such as the properties or functions other than antistaticity of the composition would be impaired.
For example, Patent Document 3 describes a polymer-type antistatic coating composition comprising a block copolymer containing a conductive segment and a hydrophobic segment. In this block copolymer, the moieties having conductivity in the polymer are accumulated by block polymerization to induce a clear phase separation to exert an antistatic effect.
However, to cause phase separation, usually a molecular weight of 10000 or more is necessary. Specifically, there is a problem that with a molecular weight less than that, no phase separation occurs, and thus cannot be used. Further, it is said to have a good solubility as it is a block polymer, while the polymers in the Examples of the reference do not dissolve in usual hydrocarbon solvents such as toluene, ether solvents such as THF, ester solvents such as ethyl acetate, alcohol solvents such as methanol, UV curable monomers such as acrylate derivatives and methacrylic derivatives, and some do not even show water solubility depending on the composition. The only possible solvent is a particular solvent such as non-proton polar solvents including dimethyl sulphoxide and dimethyl formamide. Therefore, the use thereof is limited, as it is not suitable to use in for example a non-solvent type UV curable resin, etc. or for usage where highly volatile solvent is necessary, and it can only be coated on substrate having resistance to non-proton polar solvents.
To perform additional test for the invention of the reference, the present inventors have synthesized polymers according to their method, and quaternized the polymer according to the method described in the reference. As a result, the polymer did not precipitate and became gelatinous, and the polymer could not be recovered as in the Examples of the reference.
Further, according to the reference, quaternization of polymer is performed with methyl iodide, while iodine may be the cause of coloring, and a lemon yellow coloring was generated during the additional test. Colored polymers cannot be used for applications where colorless and transparency are required such as for display.
Patent Document 4 describes a polymer antistatic agent comprising quaternary ammonium as counter cation, and it is described that the polymer antistatic agent has a superior antistatic property. However, this polymer is not a block polymer, and its molecular weight is not described.
Further Patent Document 5 describes as a composition for a golf ball, an ionomer that can be neutralized with a quaternary ammonium, specifically an ionomer having an acid on a side chain and having an acid polymer moiety neutralized with ammonium.
However, this ionomer is to improve the durability, rebounding property, abrasion resistance, etc. of the golf ball and is irrelevant with antistaticity, and it is difficult to conceive the antistatic effect therefrom. Further, it is estimated that the ionomer is a random polymer, and it is difficult that each property such as antistatic property, water repellent property, and oil repellent property is exerted at the same time in a random polymer.
On the other hand, for example, a polymer having an alkali metal salt structure of acid such as sodium salt of methacrylic acid has a low solubility and low compatibility in a composition, and the antistatic effect also tends to be low.
Further, these polymers and a composition containing these exert an antistatic function, and therefore, their surface is hydrophilic and thus the water repellency and antifouling property are poor. Further, for members of polymers etc. used for semiconductors-related products, in order to avoid performance degradation, corrosion, etc. it is said that it is necessary to control halogen atoms, as well as alkali metal and alkaline earth metal such as sodium and calcium at a ppb level, and a normal surfactant can be hard to use.
Further, recently, there is an increasing need to confer not only antistatic property but also water- and oil-repellent property and antifouling property to optical devices including displays. However, these functions and the antistatic function are contradictory, and it is said to be difficult to exert these functions at the same time.    [Patent Document 1] Japanese Laid-Open Patent Application No. 7-278400    [Patent Document 2] Japanese Laid-Open Patent Application No. 10-195422    [Patent Document 3] Japanese Laid-Open Patent Application No. 2006-104458    [Patent Document 4] U.S. Pat. No. 4,433,113    [Patent Document 5] US Patent Publication No. 2005/0288446